\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(270:1.5){A}
    \tkzDefPoint(90:1.5){B}
    \tkzDefTriangle[two angles=90 and 45](A,B)  \tkzGetPoint{T}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawPolygon(A,B,T)
    \tkzDrawPoint(O)
    \tkzMarkAngle[size=.5](T,B,A)
    \tkzLabelPoints[right](O)
    \tkzLabelPoints[below](A)
    \tkzLabelPoints[above](B)
    \tkzLabelPoints[below](T)
\end{tikzpicture}

